The flame dynamics and stabilization mechanism in a novel, ultra-lean, non-premixed, model GT burner is experimentally investigated with optical diagnostics. The burner operating with methane as fuel exhibits a convergent-divergent flow field at the burner exit. This results in two flame stabilization zones depending on the global equivalence ratios, Φglob. At 0.6<Φglob<1.0, the flame stabilizes in the diverging section where the flow field is characterized predominantly by the swirl. The strain rates in these locations are found to be well below the extinctions strain rates for turbulent non-premixed flames. With decreasing Φglob, the flame is located progressively near the burner lip, where a large recirculation zone of the central bluff body in the burner exists. The upstream marching of the flame despite a decreasing Φglob, and a corresponding decrease in heat input, is explained in terms of a flow-flame balance along the stoichiometric surface. At still lower Φglob extending to ultra-lean conditions (Φglob = 0.1), the flame stabilizes in a region characterized by bluffbody induced toroidal flow structures closer to the burner exit. © 2018 Combustion Institute. All Rights Reserved.